Gas impermeable expansion diaphragm

ABSTRACT

A hydrophone assembly for suspension below the surface of a body of water, the hydrophone assembly having a gas impervious diaphragm comprising a layer of elastomer material encapsulating a layer of metal for sealing a closed chamber which is filled with a gaseous evacuated liquid. The diaphragm compensates for changes in volume of the evacuated liquid which occurs with fluctuating temperatures and prevents any penetration of ambient air gases.

United States Patent Tallman Dec. 25, 1973 [54] GAS IMPERMEABLEEXPANSION 2,444,911 7/1948 Benioff 340/8 LF DIAPHRAGM 3,239,801 3/1966McGaugheym. 340/8 L 3,550,072 12/l970 Babikyan 340/13 R PrimaryExaminerBenjamin A. Borchelt Assistant Examiner-H. J. TudorAttorney-Louis Etlinger [57] ABSTRACT A hydrophone assembly forsuspension below the surface of a body of water. the hydrophone assemblyhaving a gas impervious diaphragm comprising a layer of elastomermaterial encapsulating a layer of metal for sealing a closed chamberwhich is filled with a gaseous evacuated liquid. The diaphragmcompensates for changes in volume of the evacuated liquid which occurswith fluctuating temperatures and prevents any penetration of ambientair gases.

8 Claims, 2 Drawing Figures l 1 R 10 :25 56 ///1 a; I E 22 1'. ,7 I aemu" ]I s as j, I so I PAIENIED DEC 2 5 I975 CHARLES V. TALLMAN ATTORNEY1 GAS IMPERMEABLE EXPANSION DIAPHRAGM FIELD OF THE INVENTION Thisinvention relates to diaphragm assemblies, and more particularly, to gasimpervious diaphragm particularly adapted for use in hydrophoneassemblies.

The invention described herein was made during the performance of acontract with the Department of the Navy.

BACKGROUND Hydrophone assemblies are commonly used in sonobuoy systemsand are used to detect the presence of underwater acoustic wavesproduced by a remotely located source. Typically, the assembly compriseshydrophone units positioned within a cavity of a housing with the cavitybeing filled with oil so as to surround and fill all voids of thehydrophone unit. The housing is then suspended from and electricallyconnected to a floating surface unit of the sonobuoy system.

The hydrophone unit is designated to generate an electrical signal whenan acoustic pressure wave strikes the hydrophone housing The oiltransmits these acoustic pressure waves causing electrical coilspositioned circuit to move thereby generating the electrical signal.During assembly of the unit, all gases have been re moved from the oilfor the presence of gas bubbles may effect the freedom of movement ofthe electrical coils. More particularly, gas bubbles may prevent or sorestrict the movement of the coil assembly as to prevent the detectionof acoustic waves. The sonobuoy system arrangements are very useful andhave been used very extensively. Sometimes, however, it may be necessaryto place the systems in storage for extended periods of time, and it istherefore necessary to provide a permanent impermeable gas barrierbetween the oil and the surrounding atmosphere.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of thisinvention to provide a novel and improved diaphragm assembly.

Another object of this invention is to provide a diaphragm assemblyhaving a metallic element molded in layers of an elastomer material.

It is a further object of this invention to provide a hydrophoneassembly which incorporates a gas impervious diaphragm for sealing achamber containing oil fromthe atmosphere for extended lengths of timeand capable of flexing to compensate for changes in the volume of theoil;

Another object of this invention is to provide a hydrophone assemblywhich incorporates a diaphragm having a metallic substance moldedbetween layers of elastomer material to provide a permanent air barrier.

According to this invention, these and other objects which will becomeapparent upon reading the specification are embodied in apparatuscomprising a flexible assembly for enclosing and sealing an open end ofa housing, the flexible assembly having a metallic substance integratedwithin a layer of resilient material.

BRIEF DESCRIPTION OF THE DRAWINGS For a clearer understanding of theinvention, reference may be made to the following detailed descriptionand accompany drawing in which:

FIG. 1 is a schematic view, partly in section, of a hydrophone-assemblyincorporating the invention; and

FIG. 2 is an enlarged sectional view of the gas impervious diaphragm.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, ahydrophone assembly, indicated generally at 10, is shown as it wouldappear positioned beneath the surface of the water at a desired depthand held there by means ofa cable 12, or by any other means well knownin the art, one end of which is secured to unit 20 at the water surface.

The hydrophone assembly structure comprises a generally cylindricalcasing or housing 22 having a bottom portion 24 and a top portion orbulkhead 25 with a central opening 26 therein, which portions close theends of the housing. Three posts, two of which are shown at 27 aresupported from the bottom portion 24 and extend upwards where they arefastened to a generally cylindrical supporting ring 28. Three additionalposts, one of which is shown at 32, extend from the supporting ring 28to another supporting ring 33 positioned closer to the bulkead 25 withposts 32 being secured to both supporting rings. Three additional posts,one of which is shown at 40, extend from supporting ring 33 to anauxiliary ring 42 adjacent to the top bulkhead 25. It will be understoodthat three posts of each group are angularly displaced in a circularpattern so that not all of them appear in FIG. 1. A pair of 0 rings 29and 34 assist in supporting rings 28 and 33 respectively in lendingstiffness to the sides of housing 22. The hydrophone sensing units,indicated generally by reference characters 43 and 44, are eachgenerally mounted to support rings 27 and 33, respectively by fourmounting brackets 45, respectively, (brackets for sensing unit 43 arenot illustrated). As explained with reference to the posts above, thebrackets are positioned in a generally circular pattern and thereforenot all of them appear in FIG. 1.

The sensing units 43 and 44 are positioned so that their longitudinal(sensitive) axis are substantially perpendicular to each other. Thesensing units may be similar to the one set forth with particularity inU. 5. Pat. No. 3,550,072, issued to .lirair A. Babikyan, assigned to theassignee of this invention. Briefly, the units include a coil comprisingmany turns of fine wire, which is supported within the housing structureand further positioned within an air gap in a magnetic circuit. Themagnetic circuit may be formed of any material which will provide asufficiently strong magnetic field across the defined air gap. The airgap of the magnetic circuit is constructed in such a manner that thelines of force forming the magnetic material are perpendicular to thelongitudinal axis of the sensing unit. Accordingly, the coil aspreviously indicated is supported within the sensing unit housing and itis arranged to travel substantially perpendicular to the lines of forceforming the magnetic field. Stated in another way, the coil is arrangedto travel in a direction parallel to the sensitive axis of the sensingunit. It follows that any axial movement of this coil attributable tounderwater pressure waves will cause an electrical signal to begenerated in the coil windings as the coil cuts the line of forceforming the magnetic field. This signal is led by means of cables 50, 51through the bulkhead 25 to unit 20 at the water surface 20. The detailsof package 20 are not illustrated since they are well known in the artand are not part of this invention.

While the above description describes the hydrophone assembly as havingtwo sensing units, it is to be understood that the number of units willdepend upon the requirements of the system and other physicallimitations.

Between the auxiliary ring 42 and the bulkhead 25 is positioned agenerally circular, flexible gas impervious diaphragm 55, a feature ofthis invention. The diaphragm 55 comprises a raised portion 56 which ispositioned within the opening 26 of the bulkhead 25. The function of thediaphragm 55 in part, is to provide a gas impermeable barrier forextensive periods of time. This is successfully accomplished as bestshown in FIG. 2 (enlarged view for purposes of clarity) by having thediaphragm comprise essentially a metal insert 57 encapsulated by asuitable, flexible coating 58, such as an elastomer. Normally, theflexible coating exhibits a greater degree of elasticity than does themetal insert, and for comparison purposes the elastomer will bedescribed as having a unit elastic limit.

Applicant has found that a lead composition characterized by itsductility and ability to undergo repeated flexing cycles, is a preferredelement for the metal insert. The physical properties of lead may befound in any metallurgical handbook. Further, applicant has found thatit is prefereable to place a fabric 59, such as Dacron, on each side ofthe lead when the elastomer is bonded to the lead in the moldingprocess. This fabric maintains the integrity of the lead, that is, thefabric protects the lead from a shearing action caused by the elastomerflowing into the mold and also provides the means for entrapped air andgasses to escape from the mold. Also, if the fabric exhibits very littleelasticity, it assists in preventing the elastomer from over stretchingduring service in the hydrophone assembly and thereby insuring that thelead will not be torn or ruptured. In this fashion, the lead retains thedesirable characteristic of gas impermeability even after undergoingrepeated flexing cycles. Still another advantage of a lead insert is itsnon-magnetic properties, a characteristic which insures that a metalinsert cannot affect the magnetic circuit in the hydrophone units 43 and44.

Further, applicant has found that chlorbutyl rubber is especially suitedfor the flexible coating 58, and its physical properties may be found ina chemical handbook. This material also exhibits a high degree ofimpermeability for a short time duration but is not by itself effectivewhen the unit is to be stored for time periods measured in months.

Describing now the function of the diaphragm 55 including the hydrophoneassembly for which it has been adapted, the interior of housing 22 andall the voids therein including the interior area of the sensing units43 and 44 are filled under pressure with a gas evacuated liquid 60, suchas oil until the assembly 10 is at a completely neutral state. Thephrase neutral state as used herein means the pressure on each of thediaphragm surfaces is equal. It is important to maintain thisestablished neutral state at all times to insure accurate and reliableoperation of the sensing units, and will be further explainedhereinafter. By this, it is meant no gaseous material whatsoever shallbe allowed to pass through the diaphragm regardless of how long theassembly 10 may be stored before use, if at all. Also, it 6 pressureagainst the surface of the diaphragm opposite the liquid. The phraseunit as used herein means that volume of liquid which will achieve theaforementioned neutral state for the assembly. Any change in the volumeof the liquid such as caused by temperature variations, causes acorresponding change in the surface of the diaphragm within thebulkheadopeningJhat is, the crown of the diaphragm may go throughseveral flexing cycles while expanding or contracting depending upon thevolume of the oil while maintaining the desirable neutral state.

Normally, when the hydrophone assembly 10 is placed into operation, itis transported by an aircraft to the particular destination. If thegasses had penetrated through the diaphragm 55 while the assembly is instorage, the gaseous material would tend to be attracted to each otherso as to form larger pockets or bubbles when the assembly 10 issubjected to less pressure at higher elevations, and these bubbles couldprevent the hydrophone assembly from operating at all.

When the sonobuoy enters the water, the cold temperatures may cause theoil to contract and the diaphragm must follow to prevent the formationof any voids or air pockets. Also, the diaphragm assists in keeping thewater from mixing with the oil.

When the sonobuoy unit is placed in the water, the hydrophone assembly10 is positioned beneath the water surface at a predetermined depthwhere pressure Waves travelling in the water strike the side 22 orbottom 24 of assembly 10, and travel through the liquid where thepressure waves cause a moveable coil in hydrophone units 43 and 44 topass through-a magnetic field at a frequency determined by the source ofthe waves and produce an electric signal which is also a function of thedirection of travel of the pressure waves. It is necessary that thesemoveable coils freely move through the magnetic field.

To insure free movement of the coils, liquid 60 is free of all gasses orgas bubbles since a gas bubble could become positioned within the fieldof travel of the coil and thereby prohibit or cause erratic movementthereof through the magnetic field. For example, if the coil fails tomove then no electrical signal would be generated; or erratic coilmovement would produce a .false signal; that is, a signal which is not atrue function of the direction of travel of the pressure waves. Thus thediaphragm must be gas impermeable for all periods of time. 1

While in the foregoing, l have described certain preferred forms andmethods of practicing my invention, it is to be understood that thisdescription is made only by way of example and not as a limitationthereon for one skilled in the art may make modifications and changesthereto without departing from the true spirit and scope thereof.

What is claimed is:

l. The combination, comprising means having a unit elastic limit forenclosing and sealing an open end of a housing, said housing having acompartment therein filled with a liquid capable of transmittingpressure waves which strike said housing;

said means being substantially parallel with a surface of said housingand responsive to changes in unit volume of said liquid; and

said means being substantially impervious to the passage of gaseouselements,.said means having a first, second and third -layers,-saidfirst and third layer having a given unit elastic limit and said secondlayer having a lower unit elastic limit, said second layer being formedfrom a metallic substance, said matellic substance being gas impervious,and

a layer of fabric positioned between said second layer and at least oneof said first and third layers.

2. The combination in accordance with claim 1 wherein said second layeris formed from lead.

3. The combination in accordance with claim 2 wherein said first andthird layers are formed from an elastomer.

4.1A pressure compensated hydrophone assembly for detecting underwaterpressure waves, comprising;

a housinghaving a compartment therein" and 'an opening at one end;

atleast one sensing unit mounted within said com partment, said sensingunit responsive to said underwater pressure waves;

a unit volume of liquid filling said compartment and voids within saidsensing unit, said liquid capable of transmitting pressure waves whichstrike said housing; and

a resilient means across said opening of said housing, said resilientmeans responsive to changes in the unit volume of said liquid andsubstantially impervious to gaseous elements, said resilient meanscomprises a first, second, and third layers, said first and third layershaving a given unit elastic limit, said first and third layers beingformed from an elastomer, said second layer having a lower elastic unit,said second layer being formed from a nonmagnetizable metal, said secondlayer being substantially gas impervious, and a layer of fabricpositioned between said second layer and at least one of said first andthird layers, said fabric providing means for gasses to escape when saidfirst, second and third layers are molded thereby preserving theintegrity of said second layer.

5. Apparatus in combination with claim 4 wherein said second layer isformed from lead.

6. Apparatus in combination with claim 4 wherein said liquid is freefrom all gasses.

7. Apparatus for detecting the presence of underwa ter pressure waves,comprising a hydrophone assembly for generating signals in response toincident pressure waves, said hydrophone comprising a housing having acavity therein and open at one end thereof;

a sensing unit mounted within said cavity, said sensing unit responsiveto said underwater pressure waves and arranged to generate acorresponding electrical signal;

a unit volume of liquid filling said cavity and voids within saidsensing unit; and

a diaphragm assembly across said opening, said diaphragm responsive tochanges in the unit volume of said liquid and substantially imperviousto the passage of gaseous elements, said diaphragm assembly comprising afirst and third layer of resilient material having a given unit elasticlimit, and a second layer of metallic substance having a lower elasticlimit positioned between said first and third layers, said second layerbeing formed from lead and being substantially gas impervious, and alayer of fabric being positioned between said second layer and at leastone of said first and third layers to preserve the integrity of saidsecond layer when said first, second and third layers are assembled intoan integral unit; and

means for maintaining said hydrophone assembly in position in the regionof the underwater waves.

8. Apparatus in accordance with claim 7, wherein said first and thirdlayers of said diaphragm are form from an elastomer.

1. The combination, comprising means having a unit elastic limit forenclosing and sealing an open end of a housing, said housing having acompartment therein filled with a liquid capable of transmittingpressure waves which strike said housing; said means being substantiallyparallel with a surface of said housing and responsive to changes inunit volume of said liquid; and said means being substantiallyimpervious to the passage of gaseous elements, said means having afirst, second and third layers, said first and third layer having agiven unit elastic limit and said second layer having a lower unitelastic limit, said second layer being formed from a metallic substance,said matellic substance being gas impervious, and a layer of fabricpositioned between said second layer and at least one of said first andthird layers.
 2. The combination in accordance with claim 1 wherein saidsecond layer is formed from lead.
 3. The combination in accordance withclaim 2 wherein said first and third layers are formed from anelastomer.
 4. A pressure compensated hydrophone assembly for detectingunderwater pressure waves, comprising; a housing having a compartmenttherein and an opening at one end; at least one sensing unit mountedwithin said compartment, said sensing unit responsive to said underwaterpressure waves; a unit volume of liquid filling said compartment andvoids within said sensing unit, said liquid capable of transmittingpressure waves which strike said housing; and a resilient means acrosssaid opening of said housing, said resilient means responsive to changesin the unit volume of said liquid and substantially impervious togaseous elements, said resilient means comprises a first, second, andthird layers, said first and third layers having a given unit elasticlimit, said first and third layers being formed from an elastomer, saidsecond layer having a lower elastic unit, said second layer being formedfrom a non-magnetizable metal, said second layer being substantiaLly gasimpervious, and a layer of fabric positioned between said second layerand at least one of said first and third layers, said fabric providingmeans for gasses to escape when said first, second and third layers aremolded thereby preserving the integrity of said second layer. 5.Apparatus in combination with claim 4 wherein said second layer isformed from lead.
 6. Apparatus in combination with claim 4 wherein saidliquid is free from all gasses.
 7. Apparatus for detecting the presenceof underwater pressure waves, comprising a hydrophone assembly forgenerating signals in response to incident pressure waves, saidhydrophone comprising a housing having a cavity therein and open at oneend thereof; a sensing unit mounted within said cavity, said sensingunit responsive to said underwater pressure waves and arranged togenerate a corresponding electrical signal; a unit volume of liquidfilling said cavity and voids within said sensing unit; and a diaphragmassembly across said opening, said diaphragm responsive to changes inthe unit volume of said liquid and substantially impervious to thepassage of gaseous elements, said diaphragm assembly comprising a firstand third layer of resilient material having a given unit elastic limit,and a second layer of metallic substance having a lower elastic limitpositioned between said first and third layers, said second layer beingformed from lead and being substantially gas impervious, and a layer offabric being positioned between said second layer and at least one ofsaid first and third layers to preserve the integrity of said secondlayer when said first, second and third layers are assembled into anintegral unit; and means for maintaining said hydrophone assembly inposition in the region of the underwater waves.
 8. Apparatus inaccordance with claim 7, wherein said first and third layers of saiddiaphragm are form from an elastomer.